The present invention relates to a jet-propulsion personal watercraft (PWC) which ejects water rearward and planes on a water surface as the resulting reaction. More particularly, the present invention relates to an exhaust structure of the personal watercraft capable of preventing water ingress into an engine when the watercraft is inverted, and of producing a high muffling effect.
In recent years, so-called jet-propulsion personal watercraft have been widely used in leisure, sport, rescue activities, and the like. The personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a hull bottom surface and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In general, in the personal watercraft, an exhaust gas from an engine for driving the water jet pump is lead to an exhaust outlet provided in a transom board through an exhaust passage including a water muffler and discharged outside the watercraft from the exhaust outlet.
The water muffler has an internal structure called xe2x80x9clabyrinth structure,xe2x80x9d capable of preventing water entering through the exhaust outlet from reaching the engine, even when the watercraft is inverted. Such a structure is especially advantageous because waves following the watercraft sometimes enter the exhaust outlet when the watercraft is inverted. In particular, in the personal watercraft with a four-cycle engine, the water ingress into the engine sometimes affects an engine power characteristic, and, therefore, it is essential that the water ingress into the engine be prevented.
Under the circumstances, Japanese Laid-Open Patent Application Publication No. 2000-282840 discloses an exhaust structure, in which a water catcher constituted by an inverted-U shaped pipe is connected to downstream of the water muffler and an exhaust gas is discharged outside the watercraft through the water catcher, thereby allowing water flowing back from the exhaust outlet to be reserved in the water catcher when the watercraft is inverted. Thus, water ingress into the engine can be effectively subdued.
However, the water catcher used in the above-mentioned exhaust structure is constituted by the U-shaped pipe manufactured from rubber exclusively for the water catcher. This is unfavorable because the manufacture of the water catcher is time-consuming which would lead to an increased manufacturing cost.
The present invention addresses the above-described condition, and an object of the present invention is to provide an exhaust structure of a jet-propulsion personal watercraft capable of subduing water ingress into an engine even when the watercraft is inverted, and of producing a high muffling effect, the exhaust structure being capable of suppressing manufacturing time and cost.
In accordance with the present invention, there is provided an exhaust structure of a personal watercraft adapted to eject water pressurized and accelerated by a water jet pump from an outlet port so as to be propelled as the resulting reaction, the exhaust structure being configured to cause an exhaust gas from an engine for driving the water jet pump to be discharged outside the watercraft through an exhaust passage, wherein the exhaust passage includes: a vertically extending water catcher having a substantially closed space in an upper portion thereof; an upstream exhaust passage having one end connected to an exhaust port of the engine and the other end connected to the water catcher at a position below the closed space; and a downstream exhaust passage having one end connected to the water catcher at a position below the closed space and the other end being opened to outside of the watercraft.
With this structure, when the watercraft is inverted, the vertically extending water catcher allows the water flowing in from the exhaust outlet opened to outside of the watercraft to be reserved in the upper portion thereof, thereby subduing the water ingress into the upper exhaust passage of the exhaust passage and the engine. In addition, since the water catcher has a relatively large capacity so as to function as a so-called xe2x80x9cexpansion chamber,xe2x80x9d a greater muffling effect can be produced.
In the invention, the downstream exhaust passage is connected to the lower end of the water catcher and the upstream exhaust passage is connected to the water catcher at a position higher than the connected position of the downstream exhaust passage. Such constitution makes it difficult that the water flowing in from the outside of the watercraft through the downstream exhaust passage enters into the upstream exhaust passage, while the watercraft is at its normal posture other than when it is inverted.
The exhaust gas from the water catcher may be discharged from the transom board at the stern of the watercraft by suitably bending the lower end of the water catcher to the rearward, or otherwise discharged outside the watercraft by connecting a suitable passage to the lower end of the water catcher.
Preferably, the upstream exhaust passage may include a water muffler, and an exhaust outlet of the water muffler may be positioned higher than the waterline of the watercraft. Such constitution also advantageously makes it difficult for the water to enter an upstream portion of the water muffler from the outside of the watercraft. Further, in the case of the water muffler having a labyrinth structure, the water entering the water muffler in the upstream exhaust passage is prevented from further entering the engine because of the structure, and the water reserved in the water muffler can be discharged outside the watercraft later, together with the exhaust gas from the engine.
Preferably, the water muffler may be placed at a downstream end section of the upstream exhaust passage which is located apart from the engine and subsequently connected to the water catcher.
Preferably, the water catcher may be adapted to discharge cooling water inside thereof at a position higher than the position where the water catcher is connected to the upstream exhaust passage, thus achieving so-called xe2x80x9cwet exhaustxe2x80x9d in which the exhaust gas inside of the water catcher is directly cooled by the cooling water.
In the invention, the water catcher may be constituted such that it includes a vertically extending outer member having a substantially closed space and an inner member provided in the closed space of the outer member so as to be apart from the outer member, and the outer member is connected to the downstream exhaust passage and the inner member is connected to the upstream exhaust passage.
It should be appreciated that the outer member and the inner member need not be completely separated as mentioned above. The outer member and the inner member should at least be constituted so as to provide a flowing space of the exhaust gas between the members. Therefore, the outer member and the inner member may be partially in contact with each other, or otherwise may be integrally formed.
Preferably, the upper end of the outer member may be sealed by a separate cap which is independently constructed from the main part of the outer member.
Preferably, the upper end face of the outer member, such as the cap, may be outwardly protruded. With this structure, the water dripping from the upper end face into the top opening of the inner pipe can be inhibited when the inverted watercraft is raised back up and the water reserved in the outer member is effectively discharged outside the watercraft.
Preferably, the upper end face of the outer member, such as the cap, may have a double-walled structure. With this structure, the vibration noise of the end face caused by the oscillating exhaust gas can be inhibited.
In the present invention, as a matter of course, the engine may be a two-cycle engine or a four-cycle engine.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.